n1 = 15
t1 = 20
n2 = 20
t2 = 10

# 首先计算两种情况下总的草量
totalGrass1 = n1 * t1
totalGrass2 = n2 * t2

# 两种情况下草量的差除以时间差就是每天新生的草量
newGrass = (totalGrass1 - totalGrass2) // (t1 - t2)

print(newGrass)